A magnetostrictive linear position measurement system typically includes a magnetostrictive waveguide wire which is housed in a protective tubular housing about which a magnet is slidingly engaged. A current pulse can be sent through a wire near the waveguide, and this pulse interacts with a circular magnetic field of the magnet to induce a torsional strain wave in the magnetostrictive waveguide at the location of the magnet. The ability of a material to deform in the presence of a magnetic field is known as magnetostriction. The strain wave travels along the length of the waveguide and passes through a coil which converts the mechanical wave into an electrical signal. To obtain the location of the magnet, the time between the transmission of the current pulse and the reception of the signal from the coil can be measured and converted to a distance, because the speed at which the torsional wave will travel along the waveguide is known. Accordingly, when the magnet is connected to a movable mass, such as a liquid level quantity or a movable element in a machine tool for example, the exact position of the mass can be measured.
Damping elements can be secured to the end of the waveguide in order to prevent the strain wave from being reflected back along the waveguide and interfering with ongoing measurements. Typically, such damping elements have been provided in the form of round rubber discs which can be compressively arranged on the waveguide wire. Also, a sleeve can be provided for supporting and centering the waveguide. One such sleeve available from Balluff Inc. includes a plurality of rigid interlocking tubular pieces having a plurality of rubber rings inserted therein for centering the waveguide. In addition, an electronics module is typically connected to the coil for controlling the transmission of the current pulse and obtaining the position measurement by timing the signal received from the coil.
A number of disadvantages have been encountered with conventional magnetostrictive position sensors. For example, the assembly of such a sensor often requires a significant amount of manual labor such as, for example, the labor required in mounting and locating the damping discs onto the waveguide, or the labor required in fitting together the various pieces and rings of the support sleeve. In addition, conventional sensors have provided no separate mounting member for the entire waveguide assembly (which includes the pulse wire, damping elements, coil, and other components), such that this complete assembly could be handled and tested separately from the final product, and prior to being assembled with the electronics module and protective housing with which it will be used. In other words, heretofore no means was provided for handling, transporting, and stocking the waveguide assembly separate from the electronics module so that the waveguide assembly could be preassembled, pre-tested, and ready for connection to a customized electronics unit and housing assembly. In contrast, conventional sensors have required delicate handling of the components until the complete unit was constructed.
Moreover, no capability was previously provided for maintaining a number of preassembled waveguide assemblies and a number of preassembled electronic assemblies on hand, and then easily connecting any such waveguide assembly with any electronics assembly to be used upon demand by the customer. Furthermore, the delicate wires of the coil and the pulse wire were not conveniently held in one fixed location for simple and efficient interchangeability with the electronics unit.
U.S. Pat. No. 4,958,332, issued to Tellerman, discloses a damping device 30 for the remote end of a waveguide wire, which includes a tubular housing and a remote housing section 34. The remote end of the waveguide 22 is held within the damping device 30 by anchor 40 and the rest of the waveguide extends from the device. Spacers 46 and 47 are provided at the opposite ends of the chamber 45 of the device 30. The spacer 47 is preferably of a soft rubber to reduce front-end reflections. The chamber 45 of the device 30 is filled with a viscous liquid damping material. The waveguide 22, along with the damping device 30 which surrounds its remote end, fits within an outer protective tube 20 which connects to a housing 12 having a mode converter. A plug 14 provides an output indicating the spacing of the magnet 17 from the mode converter in the housing 12.
U.S. Pat. No. 5,545,984, issued to Gloden et al., discloses a waveguide 4 which is partially enclosed in a suspension sleeve 2. Damping element 6 is slipped over the waveguide 4 and is generally cylindrical in shape as is the suspension sleeve 2. The waveguide 4, suspension sleeve 2, and damping element 6 reside in an enclosure tube 3 which is mechanically supported at one end by a housing 17 through an end flange 19. A suitable mode converter (not shown) provides an electrical signal to an electronic circuit 26.
Generally, however, previously available magnetostrictive linear position sensors suffer from one or more of the above-mentioned problems, including difficulty in assembly, inability to easily handle and test the waveguide assembly separate from the electronics assembly and protective housing, inability to maintain a preassembled stock of waveguide assemblies which can be quickly and easily connected to a customized electronics assembly and support housing, and/or inability to quickly and easily connect any electronics assembly with a waveguide assembly of any length Accordingly, an apparatus and method which avoids these problems would be desirable.